This invention relates to fuel additives and more particularly to additives which can improve the combustion efficiency of fossil fuels in such uses as boiler fuels and the like, as well as reducing combustible scale formation, firebox corrosion and emissions.
Fuel additives to catalytically increase the combustion efficiency of fossil fuels have been available for some time. Initially, they attracted little commercial interest because of the relatively low cost of fuel oil. In the mid-sixties the price of bunker C fuel oil was only six cents a gallon and even #2 diesel fuel cost less than twenty cents a gallon. For that reason, an up to five per cent increase in fuel efficiency was not considered sufficiently important to warrant extensive development. Today, since fuel oil prices are five or six times those of the sixties, the possibilities for increasing fuel efficiency are more attractive and are being investigated.
Nevertheless, the development of boiler fuel additives containing combustion improving catalysts have not been employed extensively by large consumers of fuel oil despite the fact that they have proven to be capable of cutting fuel bills by up to 5 per cent due to several unresolved drawbacks.
In particular, a combustion improving additive has not been provided which will also stabilize stored fuel.
A suitable combustion improving catalyst additive should promote more complete combustion and reduce deposits of carbon residue in boiler tube scale, and soot and acid smut in stack emissions. A reduction in the amount of carbon deposited on surfaces of a combustion chamber of a boiler is extremely important to the efficient transfer of heat to the boiler tubes. The build up of a layer of uncombusted materials, including carbon, on the walls of a boiler combustion chamber can have up to five times the thermal insulating value of asbestos and can very significantly reduce heat transfer. Thus a properly formulated combustion improver having this property can reduce maintenance requirements, improve heat transfer and clean up emissions, while providing more complete combustion of the carbon in the fuel, thus utilizing more of the theoretical B.T.U. content of the fuel.
In addition, any newly formulated boiler fuel additive should also be able to act as a fuel stabilizer. This stabilization is especially important with stand-by oil heating systems such as those which back up gas fired boilers in many areas of the country when extremely cold weather increases gas consumption causing line pressures to drop significantly, requiring the use of the stand-by oil fired system. Fuel oil begins to deteriorate as soon as it is produced. This presents no major problem if it is consumed relatively quickly. However, in stand-by systems, fuel may be stored for long periods and its deterioration affects both its combustibility and pumpability.
The catalytically cracked fuel oils available today age, tend to repolymerize forming submicronic particles which can plug fuel filters and atomizers. As the process continues, the repolymerized molecular weight of the particles increases, favoring the formation of agglomerates and sludge which is accelerated by the current practices. Eventually sludge renders the fuel unpumpable under the conditions of use.
The rate of repolymerization is a direct function of age and energy input into the fuel. This means that the practice of periodically pumping and filtering stand-by fuel supplies to remove sludge, as practiced by some fuel service companies, does more harm than good, unless the polymerized agglomerates are depolymerized and dispersed. Unless a suitable fuel stabilization additive having propeties which retard the formation of agglomerations is provided in the fuel, such pumping will actually hasten the repolymerization process.
Finally, bacteria present in the fuel can also create an agglomeration problem with stored fuels by providing sites for repolymerization. These bacteria feed on nitrogen, sulfur and iron oxides. Since these materials are almost always present in fuel tanks, a good biocide is also necessary in any fuel stabilization formulation.
Therefore, in addition to improving combustion efficiency, a properly formulated fuel oil additive must be able to stabilize the fuel in storage. Combustion improving fuel additives should therefore contain such ingredients as dispersants to control repolymerization, biocides to control bacteria growth, detergents to keep lines and nozzles clean, a metal deactivator to suppress copper and zinc which act as repolymerization catalysts, and corrosion inhibitors to facilitate long term fuel storage as well as providing a catalytic combustion improver.
It is an objective of this invention to provide a fuel additive for fossil fuels which promotes improved combustion efficiency as well as fuel stability during long term storage.